1. Field of the Invention
The present invention relates to a method for manufacturing an integral rotationally symmetrical metal part from composite fibrous structures in the form of fibers, fiber laps, fiber fabrics and similar, coated with metal.
2. Description of the Related Art
The importance of composite materials in the partial or total production of parts has emerged in recent years, in many technical fields, notably aeronautics, space, military, automobile, etc., because of the optimization of the resistance of such materials, for minimal weight and bulk. As a reminder, such a structure comprises metal composite fibers composed of a metal alloy matrix, by example titanium Ti alloy, within which extend fibers, for example ceramic fibers of silicon carbide SiC. Such fibers exhibit a tensile strength much greater than that of titanium (typically, 4000 MPa compared to 1000 MPa). It is therefore the fibers which take up the forces, the metal alloy matrix acting as a binder for the part, and providing protection and insulation for the fibers, which must not come into contact with one another. Furthermore, the ceramic fibers are resistant to erosion, but necessarily have to be reinforced with metal.
These composite materials can be used to produce annular, rotationally symmetrical gas turbine parts for aircraft or other industrial applications, such as rings, shafts, cylinder bodies, casings, spacers, monolithic part reinforcements such as blades, etc.
The known methods for manufacturing such integral rotationally symmetrical parts consist in superposing, around a rotary cylindrical mandrel, successive fibrous structures (fibers, fiber lap or fiber fabric) and then arranging the composite fibrous structures, wound and removed from the mandrel in a specific receiving outfit for them to be heat treated and to ultimately obtain the rotationally symmetrical part made of composite material.
For the rotationally symmetrical part to be particularly rigid and withstand forces in different directions, notably torsional forces, one of the superposed fibrous structures is oriented in a first winding direction relative to the longitudinal axis of the mandrel, then the other fibrous structure is wound on the preceding one in a second winding direction different from the first, so as to obtain two composite fibrous structures that have crossed winding directions.
However, it has been noted that crossing over the metal-coated ceramic composite fibers of the two fibrous structures superposed one on top of the other could create excessive local stresses which occur during the cooling of the part, after the creep of the thin metal cladding of the fibers of the structures. These excess stresses drastically reduce the mechanical characteristics of the part.